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The “Natural Layering Concept”: a breakthrough in free-hand bonding techniques

 

By Didier Dietschi D.M.D, PhD, Privat-docent
Senior lecturer, Department of Cariology & Endodontics, School of Dentistry, University of Geneva, Switzerland.
Adjunct Professor, Department of Comprehensive Dentistry, Case Western University, Cleveland, Ohio.
Private Practice & Edudation Center – The Geneva Smile Center, Switzerland
Address for correspondence:
Didier Dietschi
Dept. of Cariology & Endodontics
School of Dentistry
19 Rue Barthélémy Menn
1205 Geneva
SWITZERLAND

Tel: +41.22.38.29.165/150
Fax:+41.22.39.29.990
E-mail 1: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
E-mail 2: This e-mail address is being protected from spambots. You need JavaScript enabled to view it (private office & education center)

Abstract

The use of composites in the smile frame has evolved and gained maturity. However, ceramics remains the preferred aesthetic option for many clinicians because application technique still is considered intricate, sensitive and, to a certain extent, unpredictable. These drawbacks, essentially related to the complexity of many composite systems, can be overcome today with the application of the “Natural Layering Concept”, which makes use of only tow basics masses, dentin and enamel, perfectly mimicking natural tooth structure. There are plentiful indications for the use of such a simplified but aesthetically uncompromised treatment modality; actually, this approach is highly suitable for young and post-orthodontic patients where conservation of tissue is a must and in general for all patients with rather healthy dentitions.

Introduction

Composite resins nowadays occupy a paramount position among restorative materials because they offer an excellent aesthetic potential and acceptable longevity, with a much lower cost than equivalent ceramic restorations for the treatment of both anterior and posterior teeth (Osborne et al, 1990; Hickel and Mahnart, 2001; Manhart and Hickel, 2004; Macedo et al, 2006). In addition, composites restorations allow for minimally invasive preparations or no preparation at all when assuming the replacement of the decayed or missing tissues. This thinking is part of a new concept called “bio-aesthetics”, giving priority to non-restorative or additive procedures such as bleaching, microabrasion, enamel recountouring, direct composite resins, bonded bridges and implants, in case of missing dental units or more complex cases. These many procedures definitely deserve more attention because they tremendously improved in practicability, efficiency and predictability (Zachrisson ans Mjör, 1996; Croll, 1997; Heymann, 1997; Leonard et al, 2001; Ritter et al, 2002; Macedo et al, 2006; Sundfeld et al, 2007).

The creation of perfect direct restorations has been for long an elusive goal because of the imperfect optical properties of composite resins and also because of perfectible clinical procedures. The attempt to mimic the shades and layering techniques developed for ceramic restorations lead to complicated applications methods, controllable only by highly skilled practitioners. This has limited for years the number of patients who could benefit from the tremendous advantage of free-hand bonding. The use the natural tooth as a model and the identification of respective dentin and enamel optical characteristics (tristimulus L*a*b* color measurements and contrast ratio) has then been a landmark in developing better direct tooth coloured materials (Cook and McAree, 1985; Dietschi et al, 2000; Dietschi et al, 2006).

The “Natural layering concept” is a simple and effective approach to the creation of highly aesthetic direct restorations. Since the concept has become a reference in the field of composite restorations, the aim of this paper is to familiarize the practitioner with the features and clinical aspects of this new technique.

A new array of indications for free-hand bonding

Besides classical indications such as the filling of class III,IV & V cavities, many other aesthetic or functional problems can be addressed by simple, direct composite restorations (Fig.2 and 3); these indications are reviewed thereafter.

1)Post-orthodontic conditions

Lateral incisor aplasia or incorrigible canine impaction are frequent findings often approached with an orthodontic solution, following proper diagnosis of dental and skeletal conditions (Tuverson, 1970; Nordquist and McNeill, 1975 Dietschi and Schatz, 1997). However, different anatomical, functional and esthetic anomalies may result from such orthodontic approach. The increasing concern of our patients for esthetics obliges the dental team to correct these deficiencies: • unusual crown dimensions (larger or smaller )

  • unusual root diameter (larger or smaller)
  • unusual shape of the crown
  • difference in color (mainly for cuspids)
  • difference in gingival contour or level

2) Congenital aesthetic deficiencies

Due to the early preoccupation of patients for these aesthetic anomalies, a conservative aesthetic correction of these conditions is more and more mandated:

  • displasia/discolorations
  • hypoplasia
  • unsual tooth forms or dimensions
  • diastemas

3) Acquired and other aesthetic deficiencies

Many other aesthetic deficiencies in rather intact dentitions require also a conservative correction:

  • discolorations (i.e.: traumatized non vital tooth)
  • diastemas
  • abrasion, abfraction & erosion lesions
  • tooth fractures
  • caries
  • functional deficiencies

All aforementioned conditions are potential indications for conservative additive treatments, according to pre-existing tissue loss and functional status.

A new shading concept

The use the natural tooth as a model has been a logical development of direct restorative materials, leading to simplified shading and layering concept, named as the “Natural Layering Concept”. It is based on the identification of true dentin and enamel optical characteristics using tristimulus L*a*b* color and contrast ratio measurements (Cook and McAree, 1985; Dietschi et al, 2000; Dietschi et al, 2006).

Aforementioned measurements led to the following recommendations as regard optical characteristics of an ideal material aimed to replace dentin:

  • single hue
  • single opacity
  • large chroma scale (beyond the 4 chroma levels of the VITA system)

Actually, variations in a* and b* dentin values between “A” and “B” VITA shades seemed not to justify the use of distinct dentin colours, at least for a direct composite restorative system. Likewise, the variations of the contrast ratio (opacity-translucency) within a single shade group did not support the use of different dentin opacities (i.e.: translucent, regular or opaque dentins). However, the concept of a large chroma scale covering all variations of natural dentitions, plus some specific conditions like sclerotic dentin (as found underneath decays, fillings or cervical lesions) proved justified.

As regard enamel, differences in tissue lightness and translucency proved generally to vary in relation with tooth age and therefore confirmed the clinical concept of 3 specific enamel types (Ubassy, 1983):

  • Young enamel: white tint, high opalescence, less translucency
  • Adult enamel: neutral tint, less opalescence and intermediary translucency
  • Old enamel: yellow tint, higher translucency

These findings have logically designed the concept of an optimal restorative material. Dentins shades should be available in one single hue (Vita “A” or Universal dentin shade) with a sufficient range of chroma (covering at least the existing Vita shade range) and presenting opacity close to the one of natural dentin. Enamel shades should present different tints and opacity levels, tentatively replicating all variations found in nature. Typical brand names are Miris (Coltenwhaledent), Ceram-X duo (Dentsply) or as well Enamel HFO (Micerium).

Influence of the Natural layering concept on shade recording

The quality of the final restoration of course depends on a correct shade recording. According to the “Natural Layering Concept” there are only 2 basic steps involved: -1: selection of dentin chroma in the cervical area, where enamel is the thinnest, using samples of the composite material, - 2: selection of enamel tint, often performed by simple visual observation. In specific and less frequent cases, a third step might be involved in the form of a visual or photographic mapping of the tooth special optical effects (such as white hypocalcifications, high opalescence areas or areas with a higher chroma). In this situation, the application of effect materials such as white, blue or orange-gold (i.e.: Miris Effects, Coltenewhaledent) might be recommended.

Clinical application of the natural layering concept

Composites can be applied following different incremental techniques for aesthetic or practical reasons as well as for better management of polymerization stresses. The classical approach is the centrifugal technique, indicated for class III, small class IV and limited form corrections. It implies the placement in depth of one or two dentin layers (in class III cavities, 01with oblique position) (Dietschi, 1995), followed by the enamel, covering the entire surface. The other widely spread incremental approach is the bucco-lingual technique (Dietschi, 1995, 1997, 2001) (figure 3). It makes use of a silicone key made from either a free-hand mock-up (simple cases) or wax-up (advanced cases). The first layer made of enamel, is then placed directly on the silicone index so that it provides in one single step the lingual profile, width and position of the incisal edge of the future restoration. Then, dentin and effect materials (when needed) can be applied in a precise 3-dimension configuration; this provides the conditions for an optimal aesthetic result and, as well as, translucency, opalescence and halo effects.

The effect of tooth aging on dentin and enamel optical properties

A special attention has to be paid to the morphological changes which affect the incisal edge structure due to tissue aging and functional wear. Actually, in addition to the increase in dentin chroma and enamel translucency, the progressive thinning of the enamel layer and exposure of dentin at the incisal edge necessitates an adaptation of the layering technique (Fig.3E) (Dietschi, 2001).

Conclusion

Traditional restorative objectives have not changed over time; they were simply implemented by the aesthetic demands of an increasing number of patients. Composite resins then became the materials of choice for young patients and less privileged people, or in any case which requires a strictly conservative approach. The contemporary practitioner is ultimately challenged to replace the missing tissues or eventually modify their configuration by applying on the patient's teeth an artificial material, which has to simulate the appearance of natural tissues. The natural layering concept has enabled this objective to be achieved in a predictable way by incorporating newly acquired knowledge about natural tissue optical properties into contemporary composite systems. This advance can be regarded as a milestone in operative Dentistry as it will give direct composite application a tremendous input, helping a larger number of our patients to receive more conservative and aesthetic restorations.

References

Cook WD, McAree DC. Optical properties of esthetic restorative materials and natural dentition. J Biomat Mat Res 1985;19:469-488.

Croll TP. Enamel microabrasion: observations after 10 years. J Am Dent Assoc 1997;128:45S-50S.

Dietschi D, Ardu S, Krejci I. A new shading concept based on natural tooth color applied to direct composite restorations. Quintessence Int 2006;37:91-102.

Dietschi D, Ardu S, Krejci I. Exploring the layering concepts for anterior teeth. In Roulet JF and Degrange M, Editors: Adhesion - The silent revolution in Dentistry. Berlin, Quintessence Publishing, 2000:235-251.

Dietschi D, Schatz JP. Current restorative modalities for young patients with missing anterior teeth. Quintessence Int 1997;28:231-240.

Dietschi D. Free-hand bonding in esthetic treatment of anterior teeth: creating the illusion J Esthet Dent 1997;9:156-164.

Dietschi D. Free-hand composite resin restorations: a key to anterior aesthetics. Pract Periodont & Aaesthetic Dent 1995;7:15-25.

Dietschi D. Layering concepts in anterior composite restorations. J Adhesive Dent 2001;3:71-80.

Heymann HO. Conservative concepts for achieving anterior esthetics. J Calif Dent Assoc 1997;25:437-443.

Hickel R, Manhart J. Longevity of restorations in posterior teeth and reasons for failure. J Adhes Dent 2001; 3:45-64.

Leonard RH, Bentley C, Eagle JC, Garland GE, Knight MC, Phillips C. Nightguard vital bleaching: a long term study on the efficacy, shade retention, side effects and patient’s perceptions. J Esthet Restor Dent 2001;13:257-369.

Macedo G, Raj V, Ritter AV. Longevity of anterior composite restorations. J Esthet Restor Dent 2006;18:310-311. Manhart J, Chen H, Hamm G, Hickel R. Buonocore Memorial Lecture. Review of the clinical survival of direct and indirect restorations in posterior teeth of the permanent dentition. Oper Dent 2004;29:481-508.

Nordquist GG, McNeill RW. Orthodontic vs. restorative treatment of the congenitally absent lateral incisor-long term periodontal and occlusal evaluation. J Periodontol 1975;46:139-143.

Osborne JW, Normann RD, Gale EN. A 12-year clinical evaluation of two composite resins. Quintessence Int 1990; 21:111-114. Ritter AV, Leonard RH, St-George AJ, Caplan DJ, Haywood VB. Safety and stability of nightguard vital bleaching: 9 to 12 years post-treatment. J Esthet Restor Dent 2002;14:275-285.

Sundfeld RH, Croll TP, Briso AL, de Alexandre RS, Sundfeld Neto D. Considerations about enamel microabrasion after 18 years. Am J Dent 2007;20:67-72.

Tuverson D. Orthodontic treatment using canines in place of missing lateral incisors: treatment planning considerations. Am J Orthod 1970;58:109-127.

Ubassy G. Shape and color: the key to successful ceramic restorations. Quintessenz Verlags, Berlin;1993.

Zachrisson BU, Mjör IA. Remodeling of teeth by grinding. Am J Orthod 1975;68:545-553.

Figure 1:

A: Pre-operative view of a 50Y old patient with natural arrangement of teeth following bilateral incisor aplasia. B &C) Lateral views demonstrate the numerous aesthetic deficiencies such as improper space distribution, teeth forms proportions and axis, and abrasion. D & E) Post-operative view of reconstructed smile following bleaching and the use of merely additive procedures. This case illustrates the potential of conservative adhesive dentistry, also in relatively complex cases.

Figure 2:

A: Typical smile of a 60Y old patient showing important incisal abrasion and smile aging. B) After lengthening incisal edges of teeth #11 & #21, followed by recountouring of incisal edges in teeth #12 & #22, a younger and more attractive smile line is re-established. C&D) Detailed views show the rounded angles of teeth #12 & #22 which help to rejuvenate abraded smiles in a very conservative way.

Figure 3:

Build-up of 2 large class IV cavities according to the natural layering concept: A) pre operative view and shade selection with dual MIRIS® shade guide. B) free-hand mock-up which reproduce the normal length and width of the incisal edge. C) a silicone index fix this information to facilitate further procedures. D) the lingual enamels walls are built-up directly against the index E) dentin can be applied and placed precisely in relation with future incisal edge, respecting the specific tooth and age configurations. F) effect masses are applied in small quantities on top of dentin to mimic specific light effects such as opalescence (blue tinted). G) a final enamel layer has been applied on proximal and buccal surfaces to complete the restoration. H) completed restorations after tissue rehydration.

 

What Practitioners Say...

Over recent years I have attended a number of seminars and hands on courses run by Dental Events. I have never been disappointed with the quality of presenters whom have been brought to Australia. These clinicians are carefully chosen to be relevant to today's cutting edge dentistry and changing philosophies.

Examples of stellar clinicians and presenters are Pascal and Michele Magne and Didier Dietschi.

I always look forward to the next program Dental Events will organise, being confident that the chosen clinician will be of the highest quality and relevant to modern dental practice.

Dr Raymond Stabey
General Practitioner
East Doncaster
Melbourne
Victoria

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